In a municipal water system, for example, deep well pumps may raise water to the ground level to supply heavy duty surface pumps which force the water through pipelines to an elevated standpipe or water tower or other reservoir from which it is distributed by gravity flow to individual users. In such a systems, the pump is operating against a pressure head of water which, should the pump be stopped, is then by gravity urged to flow back with damaging momentum through the pump to the source from which it was removed.
Various conditions arise, such as the loss of water supply to the pump, the shutdown of the pump because of an adequate level of water in the standpipe or reservoir, a broken pump shaft or disabled motor, or a power failure or other contingency. There may be normal shutdowns or emergency shutdowns. There may be normal startup operations, or an abnormality may develop in the startup requiring an immediate emergency shutdown.
It may be further explained that three types of protective valves are commonly employed in pumping stations of the kind to which this invention relates. The first is a diversion valve, such as will exhaust air from the pump inlet to atmosphere upon startup of the pump and the discharge to waste of the first liquid reaching the pump. For example, where a deep well pump is delivering water to the heavy duty pump on the surface, air which may have filled the well shaft during shutdown is first expelled to the atmosphere and should not enter the system to which the water is supplied. Also, in this case, the water first reaching the surface may be riled and contain sand or silt, and this, like the air, is exhausted before the output of the heavy duty pump enters the pipeline. A check valve is provided between the outlet of the pump and the header or pipe to which water is received from the pump. The main function of this valve is to prevent the backflow of water under the force of gravity from the header or pipe if the pump is shut down or through some mishap, power failure, loss of suction, pump or motor damage, or simply due to a lack of demand for water from the pump. In case two or more pumps deliver water to a common header, the shutdown of one pump would divert the output of the one pump back into the water source through the nonoperating pump if such a reverse flow check valve were not provided in the output of each pump. It is to this pump and valve combination that this invention particularly relates.
The third valve usually provided in a pumping station having one or more pumps is a surge valve as disclosed in our copending application, the purpose of which is to divert a backsurge of water or liquid in the line to waste where a shock wave generated at the pumping station, such as the sudden stopping of a pump, results in a return surge of pressure, frequently of damaging proportions, unless it can be timely discharged to a waste outlet, as disclosed in our copending application referred to above.